Keyboards have been developed to facilitate entry of digital data into machines. Initially, keyboards were utilized with typesetting machines, then with typewriters and teletype machines and finally with computers and CRT displays. The entry of data in this manner is known as "keyboard entry" or "keyboarding" or simply as "typing". The display resulting from typing is called "typescript". In order to improve keyboard efficiency (that is, in order to minimize the number of strokes required to enter a given character or set of characters), several functions are usually performed by the actuation of a single key on a keyboard. Specifically, these functions may include: (a) selection of an individual character; (b) positioning the character at a specified location; (c) printing the character on paper, or displaying it on a CRT (in the description provided herein the term "printing" will refer to either of these features); (d) generation of a binary code; (e) storing a code in a buffer memory, tape or disc in machines which include such devices; (f) transmitting the code over a communication line if the machine is connected to such a line; and (g) interpretation of the code in a computer if the device is connected to such a computer.
Not all keys are coupled in the same manner. Thus, actuation of a "print" key may cause a character to be printed, coded and stored and the carriage to advance; actuation of the carriage-return key may couple the return motion of the carriage with the transmission of the contents of a buffer memory over a communications line. Still other features are employed to improve input efficiency. A key may select one character or, as in the case of the "shift" it may select a whole set of characters. To minimize the effort of positioning characters, the placement of the characters is constrained, unalterably, to an invisible grid which usually has fixed, discrete dimensions. Any character can be positioned in any grid location. The horizontal dimension of a rectangle in this grid, expressed as the number of characters per inch, is called "pitch"; the vertical dimension is the spacing between the lines. Together, these two values yield the "aspect ratio" of the output. Characters can be positioned only in the rectangles of this grid, not anywhere else. At these allowed locations, characters can be positioned either automatically (for example, by the escapement that follows actuation of the preceding print key) or manually (for example, by depressing the space bar, carriage return or backspace keys).
Although printing and positioning are separate functions, printing is usually coupled to the positioning function in conventional typewriters. This particular combination is efficient, however, only for linear text (that is, text where the characters follow each other, and further are disposed in respective printed lines). However, for two-dimensional data (for example, chemical structures) keyboard input by this means is cumbersome and tedious and requires an inordinate number of key strokes. This may be illustrated with reference in FIGS. 1, 2, and 3 and the description in the following paragraphs.
For entering simple linear text material, a typist can enter six (6) characters using (6) key strokes. For example, the word "mother" requires one (1) key stroke for each letter entered. Two-dimensional chemical structures, however, require more key strokes than there are characters in order to properly move the carriage in two dimensions. In addition, it is conventional to employ ten (10) special chemical symbols in order to type such chemical structures, these symbols being illustrated in FIG. 1. It is noted that nine (9) of the symbols represent various directionally-oriented single, double, and triple bonds. The last symbol is the so-called Luhn dot, which has conventionally been utilized to replace a carbon atom and its associated hydrogen atoms. FIG. 2 illustrates the benzene ring utilizing the Luhn dot convention to replace the six carbon atoms. Utilizing a conventional keyboard, modified by inclusion of the ten (10) special chemical symbol keys illustrated in FIG. 1, typing of the benzene ring of FIG. 2 requires thirty-four (34) key strokes. This large number of key strokes is required to type the relatively simple benzene ring structure because the standard typewriter mechanism requires multiple machine functions (such as backspace, reverse line feed, carriage returns, etc.) to be incorporated between typing of the actual symbols.
In order to reduce the number of key strokes required to enter two-dimensional chemical structures, symbols have been combined in pairs, whereby both are printed by the actuation of a single key. Symbols have also been designed to print beyond the boundaries of their display grid location, either partially or entirely. Alternatively, typists may distort input structures to make them more linear, such as the distorted benzene ring structure illustrated in FIG. 3. The number of key strokes required to type the distorted benzene ring structure of FIG. 3, using a standard keyboard modified by the inclusion of the ten (10) special keys of FIG. 1, is twenty-six (26).
An entirely different approach (used, for example, by the Chemical Abstracts Service) employs a menu of pre-established fragments to build-up a chemical structure. A subset of the menu is displayed along a margin of a CRT screen. The typist selects a desired fragment, utilizing a light pen or similar device and positions a copy of it elsewhere on the screen in the same manner. A chemical structure is built-up by repeatedly selecting and positioning fragements in this way. This method has both advantages and disadvantages. The main advantage is that entire fragments can be selected on sight without having to be assembled from individual bonds and characters. A major disadvantage resides in the fact that the limited space on the screen permits only a limited number of fragements to be displayed. Consequently, the menus must constantly be interchanged. Even so, the structure being built-up must be modified from the keyboard to substitute atoms and to enter structures not available on the menu. Borrowing from both the light pen and conventional keyboard entry technologies, this approach remains complex. Further difficulties are encountered where the free-hand drawing of a bond on the screen is necessary. Two lines, intended to interconnect, may actually fail to do so by a miniscule amount. The user may believe that they meet, but the machine will not detect it. Alternatively, a shortline segment produced when a connection is overshot, might be interpreted by the computer as a new bond. These difficulties can be avoided by constraining such input to the digital grid or by making the typist verify the computer's interpretation of the input. These constraints further reduce the appeal of this approach.